Java DIP - OpenCV Color Space Conversion

In order to change color space of one image to another using OpenCV, we read image into BufferedImage and convert it into Mat Object. Its syntax is given below −

File input = new File("digital_image_processing.jpg");
BufferedImage image = ImageIO.read(input);
//convert Buffered Image to Mat.

OpenCv allows many color conversion types, all of which can be found in the Imgproc class. Some of the types are described briefly −

From any of the color conversion type, just pass the appropriate one into method cvtColor() in the Imgproc class. Its syntax is given below −

Imgproc.cvtColor(source mat, destination mat1, Color_Conversion_Code);

The method cvtColor() takes three parameters which are the source image matrix, the destination image matrix and the color conversion type.

Apart from the cvtColor() method, there are other methods provide by the Imgproc class. They are described briefly −

Example

The following example demonstrates the use of Imgproc class to convert an image from one color space to another.

import java.awt.image.BufferedImage;
import java.awt.image.DataBufferByte;

import java.io.File;
import javax.imageio.ImageIO;

import org.opencv.core.Core;
import org.opencv.core.CvType;
import org.opencv.core.Mat;
import org.opencv.imgproc.Imgproc;

pubpc class Main {
   pubpc static void main( String[] args ) {
   
      try {
         System.loadLibrary( Core.NATIVE_LIBRARY_NAME );
         File input = new File("digital_image_processing.jpg");
         BufferedImage image = ImageIO.read(input);	
         byte[] data = ((DataBufferByte) image.getRaster().getDataBuffer()).getData();
         Mat mat = new Mat(image.getHeight(),image.getWidth(), CvType.CV_8UC3);
         mat.put(0, 0, data);

         Mat mat1 = new Mat(image.getHeight(), image.getWidth(), CvType.CV_8UC3);
         Imgproc.cvtColor(mat, mat1, Imgproc.COLOR_RGB2HSV);

         byte[] data1 = new byte[mat1.rows()*mat1.cols()*(int)(mat1.elemSize())];
         mat1.get(0, 0, data1);
         BufferedImage image1 = new BufferedImage(mat1.cols(), mat1.rows(), 5);
         image1.getRaster().setDataElements(0, 0, mat1.cols(), mat1.rows(), data1);

         File ouptut = new File("hsv.jpg");
         ImageIO.write(image1, "jpg", ouptut);
         
      } catch (Exception e) {
         System.out.println("Error: " + e.getMessage());
      }
   }
}

Output

When you execute the given example, it converts an image name digital_image_processing.jpg to its equivalent HSV color space image and writes it on hard disk with name hsv.jpg.

Original Image (RGB)

Converted Image (HSV)